For switching off currents in consumer networks, switching devices are generally used that comprise one or more current paths that in turn comprise fixed and movable contacts. The movable contacts are movable together between a closed position, in which the mutually associated movable and fixed contacts touch one another, and an open position, in which an isolating distance is formed in each case between the mutually associated movable and fixed contacts. Once the movable contacts move into the open position under a load, in other words a flow of current, arcs occur along the isolating distances. The spark duration of the arcs determines the switching time for which the flow of current between the contacts is maintained. Further, the arcs release a large amount of heat, which leads to thermal destruction of the contacts and of parts of the switching chamber in the direct vicinity of the contacts, and thus to a reduction in the service life of the switching device. It should therefore be aimed to quench the arcs as rapidly as possible, this being possible for example by way of arc quenching devices. By way of these quenching devices, the arcs are for example divided into individual sub-arcs. Once the total of the sub-arc voltages is greater than the driving voltages, the arcs are quenched.
In switching devices for DC applications, the arc is not interrupted automatically, as would be the case for each zero of an alternating current. Therefore, in DC applications, blowing magnets are used, which generate a directed magnetic field in which the arcs are deflected due to the Lorentz force, which is used to drive the arcs to the arc quenching devices. In the quenching devices, the arc voltage is increased by extending and cooling the arc and dividing it into sub-arcs, resulting in the arc being quenched.
A corresponding switching device, suitable for DC operation, is known for example from EP 2 747 109 A1, in which a quenching device for quenching an arc is provided, comprising a first running rail arrangement for conducting an arc having a first current direction and comprising a second running rail arrangement for conducting an arc having a second current direction into said quenching chamber. The two running rail arrangements each have a first running rail and a second running rail, the two first running rails extending from a fixed contact in opposite directions and the two second running rails extending from a movable contact in opposite directions. To provide a switching device that has a high service life even if high-energy switching arcs occur, for example in a highly inductive circuit, it is proposed therein for the first running rails to be electrically conductively interconnected in the form of a closed loop. In the presence of high-energy switching arcs, in particular if there is a large inductive portion in the circuit, it may occur that an arc that enters the quenching chamber only loses part of its energy therein and is not yet fully quenched. In this case, arc-backs may occur after it passes through the quenching chamber, in such a way that the arc subsequently commutes from the outer end of the quenching chamber to the end of the running rails and in some cases runs back toward the contacts. Depending on the shape of the switching chamber, the arc may also burn in place at some points, for example at the end points of the running rails, leading to a correspondingly increased arc spark duration and thus an increased thermal load on the switching chamber, which can thus lead to a reduced electrical service life for the switching device.